Tuesday, March 19, 2013

Flattening Glued-up Panels

Sorry it's been a while since the last entry! Things have been crazy at work, but I'm still working wood and I still have plenty more to share with you guys, so please bear with me. I've been tracing the process of making a countertop. That has actually been done for a month or so, and I installed it on top of a run of cabinets in my shop. So today I'll backtrack a bit to cover flattening a big panel.

After using the router to joint the boards, glue-up was a snap, and I got glue joints as clean as I've ever gotten on boards as long and thick as this. I was so excited about how nicely the boards went together that I didn't use clamping cauls, and the completed countertop wasn't as flat as I'd normally expect. As a result, I had lots of work to do flattening the thing.

Years ago I saw Toshio Odate demonstrate flattening wide planks with a hand plane and he had no patience for people who wanted to use winding sticks or other devices to tell them where to remove wood. “Just look at it! Plane down the high spots!” (that's a rough paraphrase, but it's pretty close to what he said.) I think he's right, if you get plenty of practice. But I don't do this every day, or even every month, so I work on the high spots for a little while, and then check my work. For me, it's more important to take a little extra time and get a good result. Sometime in my life I may have more regular practice at this, and I promise to do it by eye at that point!

A 32” wide by 90” long countertop, 1-7/8” thick, is too heavy to lift and put into a planer, even if you have one wide enough. I have run things about this size through my old Performax drum sander, but I was much younger then (and even then, my back was killing me aferwards). If it's this big, I much prefer to let the workpiece sit still and bring the tool to it.

I don't care if you use one of these,

Or one of these,

Or these,

Or something else entirely like a belt sander. The principle is the same: remove wood from the high spots, and the high spots only, until your workpiece is flat. A workpiece this long and wide is so much bigger than the tool being used that you need a nice long straightedge to keep track of that. Here's mine:

but there's nothing special about it, it's just long and straight. Lay it down here and there to see where it's touching. If your piece is WAY out of flat, that will be easy to see. Here's how it looked early in the process. You can see the big gaps where the straightedge isn't touching.

Later on, it's harder to see where the high spots are, because you have large flat areas that are only slightly higher than the few remaining low spots. Once you reach this stage, I have an easier time if I use something really thin under the straightedge to see where it's touching and where it isn't. Writing paper is only a few thousandths of an inch thick, so it's a very good indicator.

Wherever the paper sticks under the straightedge, is a high point. Mark the high areas with pencil, all over the piece, and plane or grind or slice wood off until all your pencil marks are gone. 

Then check the whole surface again. It's a simple process, and can get monotonous, but is very satisfying. Working on a big piece like this is a good way to develop your hand plane technique. Also your sharpening technique. These are good things.

A couple of pointers:

If the face you're working on is convex, don't take any wood away from the outside edges until the very end. This is one place I agree with David Charlesworth: you'll do more accurate work if you aim to produce a very, very, slightly concave surface.

When you do this with a hand plane, it's quickest to work perpendicular to the grain, which isn't an intuitive way to work for some people. However, the shavings actually come off more easily if you cut across the grain, and you tend to get less bad tearout. On the other hand, the surface you leave is rougher, almost fuzzier.

Here's something I learned on this job: working across the grain with a power planer creates shavings that choke the vacuum hose! Not sure why, I think they tend to be longer than the shavings you create by cutting along the grain.

Producing an intact, very thin shaving across the grain is a pleasure. Look at this beauty:

And you can tell by the way it tapers off at the edges that I have an appropriate amount of crown on the blade.

Go make stuff! See you next time. I'll probably cover installing the cabinets under this counter. 

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